Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

059
FXUS63 KLOT 141115 CCA
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
600 AM CDT Sat Mar 14 2026

.KEY MESSAGES...

- There is about a 20% chance for some areas to pick up a
  dusting of snow today.

- Waves of showers and thunderstorms may occur on Sunday. There
  is a Level 2 out of 5 threat for severe thunderstorms Sunday
  afternoon mainly east of Interstate 55. The primary threat is
  damaging winds.

- A period of accumulating snow accompanied by northwesterly
  winds gusting over 40 mph may occur Sunday night into early
  Monday, mainly northwest of Interstate 55.

- A period of cold temperatures is expected Monday and Tuesday,
  with overnight wind chills ranging from 5 to 15 below,
  especially Tuesday morning.

- The period of cold temperatures should be brief with warming
  temperatures by the end of next week.

&&

.DISCUSSION...
Issued at 304 AM CDT Sat Mar 14 2026

Through Tonight:

Early this morning, low- to mid-level frontogenesis within a
northwest-southeast oriented baroclinic zone has caused multiple
snow bands to flare up on regional radars from South Dakota
down through central Illinois. Much of these radar returns are
reflective of virga at this time with a wedge of dry air below
700 mb chewing up the descending snowflakes before they can
reach the ground, though there is at least one exception to this
with a few ASOS sites in southeastern and central South Dakota
reporting snow from a relatively elongated band at the time of
this writing.

A similar story should continue to play out through the early
afternoon today as the f-gen circulations powering these snow
bands drift through our area. Most snowflakes will continue to
be sublimated before they are able to reach the ground, but
wherever frontogenetical forcing is strongest/most persistent
and mid-level lapse rates are steepest, snowflakes will have a
better chance to penetrate the dry layer and reach the ground
across a narrow spatial corridor. Thus, with the continued
lower-end likelihood for some localized dustings of snow
accumulation to occur and the expectation that most locations
will not see any accumulating snowfall today, the going slight
chance PoPs in our forecast grids continue to look appropriate
for the situation. Any snow that does accumulate will likely
only do so on grassy and colder surfaces, given that air/ground
temperatures have largely remained above freezing recently and
that air temperatures today should generally be in the
mid-upper 30s during any precipitation.

Tonight, warm air advection will really start to ramp up as the
incoming weather system for Sunday/Monday starts to get its act
together over the central/northern Plains (more on that in the
long term portion of the AFD below). Increasingly breezy
southeasterly winds will result in a non-diurnal temperature
trend into Sunday morning with surface temperatures expected to
rise after midnight. A deepening mid-level cloud deck and
steepening mid-level lapse rates may also support the
development of precipitation somewhere over our forecast area,
but at this time, it appears that the most likely outcome is
that any measurable stratiform or convective precipitation that
develops should remain to the north and northeast of our CWA.

Ogorek


Sunday Onward:

The primary focus in the long-term period is on the strong
synoptic-scale cyclone that will bring a myriad of impactful
weather to our area tomorrow and Monday.

Over the next 24 hours, an upper-level shortwave moving onshore
into the Pacific Northwest will undergo significant
amplification wile diving southeastward across the central
United States. Ensemble model guidance remains in excellent
agreement that the initial surface cyclone will develop in the
lee of the Rocky Mountains near the WY/SD/ND border region
today, move eastward across northern Nebraska tonight and
across Iowa tomorrow morning, and then shift along or just
south of the Illinois/Indiana border tomorrow night before
lifting toward Michigan on Monday. A broad region of upper-
level diffluence within coupled jet streaks will facilitate the
rapid deepening of the low as it moves into the Great Lakes
tomorrow, with ensemble mean pressures falling toward 990mb
(individual ensemble members falling into the mid to upper
980s).


High Winds:

As the low moves across Iowa and eventually toward the
Mississippi River tomorrow, impressive pressure falls in the
Great Lakes on the order of 12mb/6hr will cause low-level
southerly flow to rapidly intensify in the warm sector of the
approaching cyclone. Indeed, deterministic HRRR/RAP output
depicts 925 and 850mb flow increasing to 50kt to 60kt,
respectively, by early tomorrow afternoon (and even higher by
the evening). While such strong flow will advect an EML plume
northeastward into the Lower Great Lakes atop the warm sector,
forecast mixing profiles depicting momentum transfer from the
925mb wind field supports a legitimate threat for surface gusts
to routinely hit 55 to locally 65 mph in the warm sector
particularly with eastward extent where the impacts of any low-
level stratus should be minimized and surface temperatures will
be warmest. So, will go ahead and hoist a High Wind Watch for
damaging southerly wind gusts for areas along and east of I-55
from mid-morning through the evening. Will note that if forecast
confidence is not quite there to convert the High Wind Watch to
a High Wind Warning in later shifts, we almost certainly will
need a Wind Advisory for the same area (as well as further to the
northwest).


Severe Weather Threat:

Outside the strong synoptic winds, being in the warm sector of
deepening cyclones this time of year often brings consequences
in the form of severe thunderstorms. The first opportunities for
thunderstorms on Sunday will be during the morning hours
primarily across Illinois, as an apparent mesoscale gravity wave
activates the EML plume into a northeastward-band of convection
(nearly every CAM has this signal). While steep mid-level lapse
rates intersecting the minus 10 to minus 30 layer will promote
the development of hail, convective-layer shear looks relatively
meager during the morning (only about 20 to 25 kt). Accordingly,
the main threats with any morning convection should be spits of
pea to dime size hail. Suppose there could be bouts of locally
damaging winds where any convection is able to mix down the
strong low-level wind field (doesn`t quite look like a true
signal for damaging wind-producing GWAC), so confidence is
higher in the production of sub-severe hail.

During the late afternoon and evening hours, the surface low
pressure system will move along or just south of the Illinois
and Wisconsin border leading to further intensification of the
low-level wind field (850mb flow progged to rocket toward 70kt).
There continues to be a signal that a narrow ribbon of low-
level moisture will stream northward and just ahead of an
eastward-moving cold front, setting the stage for a high-
shear/low-cape (HSLC) severe weather-set up. The northern extent
of these kinds of set-ups are notoriously difficult to discern,
and can sometimes depend on literally every degree of both the
surface temperature and dew point. Nevertheless, the signal for
strong low-level convergence along the front continues to
garner concern for a low-topped squall line (with or without
lightning) to develop along the cold front near the Mississippi
River Sunday afternoon and then sweep across the area during the
evening with a threat for damaging winds. The Storm Prediction
Center outlook featuring level 1 and 2 threat areas across our
area, highest with eastward extent, continues to look
appropriate. (Often, synoptic winds increase markedly in the 1
to 2 hours preceding the passage of strongly-forced squall lines
in these regimes, as well).


Winter Weather Threat:

Sunday night into Monday, the low pressure system will lift into
Lower Michigan. Expansive upper-level diffluence in the left exit
region of an impressive 125kt 500mb jet streak lifting into the
Lower Great Lakes will allow the surface low to continue rapidly
deepening (toward the lower 980mb range?) as well as support the
development of a "comma head" precipitation region along the
backside of the low. Precipitation type should change from rain to
snow as temperatures tumble behind the system, though a 2 to 3 hour
period of a wintry mix cannot be ruled out as the transition occurs.
The southern extent of the snow on the backside of the system
remains somewhat varied in model guidance, likely owing to subtle
differences with exactly how fast and where the low matures. Indeed,
ensemble IQRs for snowfall from the EPS and GEFS at Rockford range
from 1 to 6 inches, with tails reaching double-digit totals. With
that said, there is a reasonably strong signal that measurable if
not plowable snow will be observed across parts of our area,
favoring those northwest of I-55. Note that a dusting to an inch may
still fall elsewhere across the area.

Snowfall totals are rarely the only entity that makes wintry
weather impactful. Indeed, impressive pressure rises along the
backside of the system around 10 mb/6hr (by virtue of a 1030mb+
surface high settling in the northern Plains) suggest that
northwesterly winds will quickly pick up and routinely gust 40
to 50 mb as the snow is falling and low pulls away. Snow
character should start quite wet with a ratio near 10:1, which
may initially limit accumulations on the wet/road ground.
However, the rapidly cooling low-level thermal profile will
allow snow to become increasingly more fluffy with time. So,
conditions should become more hazardous with time, particularly
after midnight Sunday night. Snow should then taper from south
to north throughout the day on Monday as the low pulls away.

Headline decisions for the winter portion of the event are not
straight forward, especially considering we are now about 48
hours away from when the first snowflakes would fall. Normally,
we use 6 inches of snow in 12 hours as an "entry point" to
consider a Winter Storm Watch, and then use other factors such
as temperatures, wind speeds, and time of day to ultimately
leverage a decision. With this particular system, the eventual
snow accumulations may struggle to reach that 6 inch entry
point, though the potential overlap of strong wind gusts with
falling snow leads to a heavy pull toward needing a product.
All things considered, will issue a Winter Storm Watch for Lee,
Ogle, Winnebago, and Boone Counties where confidence is the
overlap of plowable snow and strong winds is currently highest.
With that said, can easily envision an off-ramp to issue a
Winter Weather Advisory instead of a Winter Storm Warning if it
does look like we`re looking more at a 2 to 4 inch snowfall
versus 4 to 6+ inch event. Note that conditions may remain
hazardous even after snow is done falling due to blowing and
drifting due to the continuation of strong northwesterly winds.


Rest of the long-term period:

Monday night into Tuesday will feature a brief hit of chilly
air as unseasonably cool 850mb temperatures bottoming out near
-20C slosh into the region behind the departing storm system.
Lows Monday night are expected to fall into the single digits
which, with continued gusty northwest winds, will feel more like
5 to 15 below zero. Ensemble guidance hints at a threat for a
clipper-like system in the Tuesday night to Wednesday timeframe
before a warming trend becomes reestablished across much of the
country by the end of the week.

Borchardt

&&

.AVIATION /12Z TAFS THROUGH 18Z SUNDAY/...
Issued at 548 AM CDT Sat Mar 14 2026

A surface high pressure system currently centered over the Great
Lakes will shift eastward throughout the day, allowing for
winds to settle on an east to southeasterly direction will
gradually increasing in magnitude toward 10-12kt. Various mid-
to upper- level clouds and virga will stream overhead through
the day associated with ephemeral frontogenesis acting upon a
northward-moving baroclinic zone. There is a low (10% or so)
chance that snow makes it to the ground at some point this
morning, though any accumulations should be minimized to a
dusting at worst.

Tonight, winds will turn more southeasterly and increase in
magnitude in response to initial pressure falls in the Great
Lakes ahead of a developing storm system in the northern Plains.
A southerly low-level jet will develop and intensify toward
45-50 kt with time, leading to LLWS criteria being threatened
(including a 30 deg directional change).

After daybreak, winds will turn south to southwesterly and
increase in speed with gusts approaching 30 kt by mid-morning.
The eastward advection of a plume of mid-level lapse rates and
increasing low-level warm air advection will support the
development of a few showers and storms toward late morning. So,
will introduce PROB30 groups for the last 3 hours in the
outgoing ORD/MDW TAFs.

Borchardt

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Winter Storm Watch from Sunday evening through Monday evening
     for ILZ003-ILZ004-ILZ008-ILZ010.

     High Wind Watch from Sunday morning through Sunday evening for
     ILZ023-ILZ032-ILZ033-ILZ039-ILZ108.

IN...High Wind Watch from Sunday morning through Sunday evening for
     INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Gale Watch from Sunday morning through Sunday evening for the
     IL and IN nearshore waters.

     Small Craft Advisory until 10 AM CDT this morning for Gary to
     Burns Harbor IN-Burns Harbor to Michigan City IN.

&&

$$

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